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Just as your green beans will get greener when you blanch them in a pot of boiling water, so will basil. Following that logic, for greener basil send the leaves into boiling water (then shock them in an ice bath to stymie the cooking process).

But what the pesto people cannot reach a consensus on is how much the blanching affects the overall product: Does it give a less flavorful sauce? The answers are mixed. While most agreed that blanching the basil dulls its flavor to some degree, the extent is contested.

The blanchers

Fine Cooking calls basil-blanching "The Trick to Smooth, Creamy Pesto." Blanching is not solely for cosmetic purposes, but also for textural reasons: Cooked basil will emulsify more easily, resulting in a smoother sauce. "Blanching will slightly reduce the potency of the fresh basil flavor, but because a good bunch of basil starts out so incredibly fragrant, the reduction is minimal."

"Doing this leaches out a wee bit of the basil’s vivid flavor, but not enough to change that of the pesto significantly," writes Martha Rose Shulman in her recipe for Bright Green Pesto on the The New York Times.

I was amazed at how much flavor the blanched basil retained, and how green my pesto was even after days in the fridge! I was a convert. I also found that, just like with fruits and vegetables, blanching my basil before freezing it made a world of difference.

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The blog "Food and Style" lauds blanching as a method for "all of the flavor, none of the funky brown color" and is adamant on the flavor retention: "You may think that blanching the basil will take away some of its spunk, but be assured that it doesn’t. Indeed, the technique won’t take an ounce of flavor out of the aromatic leaves."

And so does Tom Colicchio. Yes, even Tom Colicchio blanches! (Cue gasps.) "But if you make pesto my way—blanching the basil quickly and shocking it in ice water—you'll find that it stays bright green and that it tastes every bit as fresh as when it's made with raw basil. It even keeps the same, big, fresh aroma."

The difference is obvious!

The skeptics

The Kitchn tested the tip and declared it "mind-blowing... but with a caveat": "The winner here? Unblanched pesto by a mile. It tasted herbaceous, fresher, and well, like fresh basil. The blanched pesto's flavors were muted, and to be honest, didn't really taste like basil anymore." But, they conducted their taste with a 15-second blanch, much longer than Martha Rose Shulman (and others) suggests.

Daniel Gritzer, writing about pesto pasta for Serious Eats, is firm about the most important rule of cooking with pesto: "Don't cook it." We must assume that this applies to the leaves themselves, too.

In a departure from almost every other pasta sauce out there, all the charm of pesto is dependent on its fresh, raw flavor. Heat, and in particular prolonged exposure to high heat, is just about the worst thing for it. That's why most store-bought pesto is so disappointing: The high-heat sterilization necessary for canning and bottling cooks the basil, turning its volatile anise-mint scent dull.

But in another article, this one called "The Best Pesto," he concludes that "Because pesto is such a strong sauce, anything you do to reduce its pungency just a little and steer it towards a sweeter, rounder-flavored sauce, will help." That leaves the question, not addressed in that post, up in the air: Does blanching tone down the sauce, or make it less herby and more garlic- and cheese-forward and therefore sharper and more biting?

No one argues that blanching does *not* make the pesto brighter and greener.

The difference in color was remarkable and most of us thought the taste was, too. The pesto made with raw leaves was herbier, with an immediate and earthy basil flavor; the basil in the blanched pesto was more mellow, leaving more opportunity for the garlic, cheese, and salt to come to the forefront: It was flavorful, but not particularly from the basil.

Blanched pesto smeared on the left; raw pesto on the right.

Ultimately, most of us preferred the raw. (Sorry, Tom Colicchio.) But our photographer Bobbi could barely taste the difference, and said she would definitely blanch for the greener color alone.

My personal conclusion: I'd skip the blanching if planning to serve (or consume) the pesto that same day. But if I'm going to store it in the refrigerator (or the freezer) for some time, where it will continue to oxidize, the flavor degrading anyway, that's when I'd consider blanching first.

A student of English, a lover of raisins, a user of comma splices. My spirit animal is an eggplant. I'm probably the person who picked all of the cookie dough out of the cookie dough ice cream. For that, I'm sorry.

I'd never blanch basil (or other green herbs). At most, NuMystic & CV, my first thought after reading this article was to blanch part of the basil and blend it with fresh unblanched. You get the best of both the dark green world and the best of the super fresh natural basil aroma and taste. If using pesto with hot pasta or other cooked/hot food, I imagine the heat is going to affect the pesto to a certain degree (in color, aroma & flavor). Seems like an extra step for almost nothing in return. I'm perfectly content not blanching basil.

I also put oil on top of my pesto to stop oxidation. If I scoop any out I even it out in the container and try to cover it each time with a bit more oil. I might try blanching if I wanted to make a particularly smooth and less pungent pesto. These days I usually make a 4 herb pesto depending on what's available in the garden. It's rarely all basil even in the summer time. Oil works great. My pesto is much brighter than either of the pics and the oil keeps it that way.

I have not tried this but I think I'll avoid it. Basil is easily rendered "grassy" by heat. Even adiabatic heat can do it. You can use some of the modernist stuff to keep the basil bright green and preserve the flavor of fresh leaves.

One option not mentioned here is to blanch half of the basil. That way you get a combination of the strong flavor of raw basil with some of the color retention/longevity characteristics from the blanched leaves.

In a way, it's like cooking a dish with fresh herbs, then adding some more fresh stuff right at the end as a garnish.

Good Morning Sarah, firstly lets add Blanch and Pesto to the vast list of cat names. Moving on, I do not blanch my pesto, because I am lazy and like your article about being the best cook you can be, it's not worth the extra effort. Also, I use it immediately and freeze the rest. Yes it can get dark but I am okay with that and usually I am adding it to something else anyway. Pesto screams it's presence on the first bite you taste, no need for the fluorescent green glow.